A known method of laser cutting patterns in material is to advance a finite length of material into a cutting zone, and while the material is stationary, using a laser beam nozzle mounted to a X-Y positioner for emitting a laser beam to cut the pattern from the material.
The numerically controlled positioner positions the laser beam over the material in response to a predetermined known pattern. Once the pattern is cut the conveyor advances to eject the cut pattern and bring new material into the cutting zone.
Increases in throughput have been achieved by implementing multi-ply cutting, increasing the speed at which the laser moves and using rapid conveyor movement to eject material.
In Canadian Patent Application published in Canada as application number 2,016,554 in Nov. 11, 1991, a method is disclosed which partially achieves the objective of increasing the throughput of cut patterns by enabling laser cutting while material is moving in a continuous manner through the positioner laser cutting zone. This "Cut-on-the-Fly method provides two-fold savings: it eliminates the loading and unloading of material from the cutting zone; and it takes advantage of movement of the cutting head along the axis of the conveyor as well as across the conveyor. The conveyor and the fabric is passed through a rectangular (X&Y axes) cutting zone of finite dimensions. A laser nozzle is suspended from an X-Y positioner. The heavier laser itself is located remote from the positioner. The positioner is movable in X and Y axes for manipulating the laser nozzle and emitted laser beam within the cutting zone. A computer directs the positioning of the laser nozzle, its velocity and its acceleration. The laser nozzle is required to stop at each non-tangent intersection of discrete moves. The nozzle cannot accelerate through a curve.
The fabric is cut according to patterns specified in a data file. The conveyor moves through the cutting zone continuously, The laser beam must cut the pattern before the fabric leaves the cutting zone. The speed at which cut fabric may be produced is dependent upon factors including laser power, the physical speed at which laser nozzle can be manipulated through the cutting zone and optimization of the sequence of the cuts made so as to minimize wasted (non-cutting) movement and to ensure continuous movement of the conveyor. Accuracy of the cut, and hence the accuracy of the geometry of the pattern, is dependent upon the physical resolution of the positioner and the nature of the instructions given to the positioner.
The positioner used with the Cut-on-the-Fly apparatus described above employs a gantry which manipulates and positions the laser nozzle. Stepper motors are used to incrementally move the gantry along the X-axis and a stepper motor drives the laser nozzle along the Y axis. One stepper motor is used for X-axis control and is located on one end of the gantry.
Several issues arise when using stepper motors in moving a laser nozzle. First, the stepper motors do not provide the high resolution need for precise control, particularly at high speeds. Stepper motors are relative positioning devices, i.e. increment three steps from this position. As a result, the controller will still be feeding absolute coordinates to the positioner, but the stepper could have inherited an offset and are subject to slipping at high speed. The steppers become less effective as the demand for greater speed increases. The force produced by stepper motors is maximal at rest and falls off as the stepper speed increases. With the demand for greater and greater speeds, a stepper motor is pressed into service at its worse operating range, where little force is available to effect rapid changes in velocity. Further, if the laser nozzle is at the opposing end of the gantry from the stepper motor, then mechanical lag can result when driving the laser nozzle along the X-axis.
Accordingly, it is known in the prior art to provide:
An X-Y axes positioner upon which the lens and mirrors of a laser are suspended for issuing a laser beam to cut underlying material; PA1 incremental or continuous conveyor movement for passing material beneath a laser cutting means; PA1 user of stepper motors to control gantry movement; PA1 use of a geometry set from which the pattern is determined, cut lines are calculated and optimization of the cutting sequence is performed; and PA1 use of a computer program to direct the laser position and coordinate laser position and continuous conveyor movement. PA1 b. avoiding starting and stopping the laser nozzle movement, associated with lost time to decelerate and accelerate the nozzle; PA1 c. avoiding high velocity during repositioning of the laser nozzle which can exceed the limited power laser's ability to cut the material, resulting in missed threads or uncut zones. PA1 a. minimizing the time for "dry haul", that is, where the laser beam is not actively cutting but is merely being re-positioned; PA1 b. planning to cut lines to cut the perimeter of the space between the patterns as opposed to the greater traversed distances for cutting the perimeter of the pattern itself; and PA1 c. predetermining the optimal cutting sequence. PA1 improved positioner structure; and PA1 improved positioner feedback. PA1 modifying the tool path to minimize stop and go; PA1 modifying the tool velocity profile throughout the path to minimize time while adhering to limitations including maximum tool acceleration, velocity and being cognizant of integer values for position and time; and PA1 controlling conveyor movement to ensure continuous movement and continuous velocity across bites. PA1 1. the inertial limitations of the positioner; PA1 2. the maximal velocity of the tool--in the laser and fabric context, being constrained by the relationship of laser power and the ease in which fabric can be cut; PA1 3. the incremental integer movement resolution of the X-Y positioner; and PA1 4. the incremental integer time resolution of the digital controller for processing positioning control signals for directing the X-Y positioner.
Challenges associated with cutting continuously moving materials include: p1 a. directing the positioner to cut along all of the cut lines on the material before the material moves out of the cut zone;
In is known to perform certain optimization by:
In order to increase the throughput of the system the positioner movement can be further optimized by both minimizing stop and go, enabling acceleration through a curve, avoiding exceeding maximum velocities and accelerations, and by modification of the positioner to enable high acceleration while maintaining accurate positioning.